The Collaborative International Dictionary of English v.0.48:

claxon \claxon\ n.
   a kind of loud horn formerly used on motor vehicles.

   Syn: klaxon.
        [WordNet 1.5]

The Collaborative International Dictionary of English v.0.48:

claxon \claxon\ v.
   to sound loudly; -- of car horns.

   Syn: honk, blare, beep, toot, klaxon.
        [WordNet 1.5]

   2. to use the horn of a car.

   Syn: honk.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

claxon
    n 1: a kind of loud horn formerly used on motor vehicles [syn:
         klaxon, claxon]
    v 1: make a loud noise; "The horns of the taxis blared" [syn:
         honk, blare, beep, claxon, toot]
    2: use the horn of a car [syn: honk, claxon]